Sulfur dioxide discharged from industrial processes is the major source of acid rain and sulfur dioxide pollution. In order to control sulfur dioxide emission to improve environmental quality, industrial flue gas desulfurization is necessary and must be enforced.
Acid tail gas generally refers to the tail gas generated from the following steps: a sulfur-containing gas generated from the chemical (especially coal chemical) process firstly goes through the recovery process to recover sulfur, phenols, naphthalenes and so on, and then is sent to the incinerator to fully combust the organic compounds and hydrogen sulfide. The main hazardous component in the acid tail gas is high-concentration sulfur dioxide, which needs to be treated in the desulfurization unit in order to meet the emission regulations.
In the coal chemical industry, the Claus sulfur recovery process is usually used for removing hydrogen sulfide and recovering sulfur. In order to ensure that the tail gas meet the emission standards, the SuperClaus, EuroClaus or SCOT technology is usually used to treat the tail gas from the conventional two-stage Claus sulfur recovery unit. All these processes have the disadvantages of complicated process, high investment, high operating cost, difficult operation or the like. For example, CN200710049014 improves the low-temperature Claus sulfur recovery process by mixing an acid gas and air for Claus reactions to take place inside the combustion chamber, and using the process gas from the first stage of the waste heat boiler as the reheating source. This invention contains a gas-gas heat exchanger, which utilizes the process gas at the first stage of waste heat boiler, or the flue gas at the outlet duct of the incinerator at 600° C. as the reheating resource for the subsequent reactors. The second stage to the fourth stage reactors and the third stage to the fifth stage sulfur condensers are controlled by a switching valve program. In each switching cycle, two of the three reactors undergo low-temperature absorption while the other reactor undergoes temperature ramp up, stable regeneration, gradual cooling, and stable cooling. Such control is complicated, and if stable control cannot be achieved, the sulfur recovery efficiency will be greatly affected.
Sodium carbonate and sodium hydroxide are used previously for the removal of sulfur dioxide from acid tail gas in small-scale chemical processes. This method also has the disadvantages of high capital and operating costs, and complicated operation or the like. Coal chemical industry which uses atmospheric fixed-bed gasifier with lump coal as raw material often uses atmospheric pressure desulfurization technology by installing an absorber operated at atmospheric pressure (20 kPa) in the coal gasification process. At present in China, the circulation and regeneration of kauri solution is often used for desulfurization, and then the sulfur recovery devices are used to generate sulfur.
At present, limestone desulfurization is widely used for treating flue gas from coal-fired boilers. Capital and operating costs for limestone desulfurization device are high, and especially, it requires high-quality limestone, and the market for the desulfurization byproduct (gypsum) is limited. Waste water generated from this process has to be disposed. Sodium carbonate and sodium hydroxide desulfurization, which is often used in acid tail gas desulfurization treatment, consumes sodium carbonate and sodium hydroxide, and the market for its byproduct sodium sulfate is limited, resulting in high operating cost and poor reliability.
With the wide applications of ammonia desulfurization technology, the advantages of this method become more and more significant. Benefiting from its advantages such as high efficiency, no secondary pollution, byproduct recycle, simple process, and integrability with boiler flue gas desulfurization, the ammonia desulfurization technology can be applied to more industrial processes. For example, in coal chemical industry, two-stage Claus sulfur recovery can be combined with ammonia desulfurization, achieving over 99.5% desulfurization efficiency\and 95% sulfur recovery. The byproduct ammonium sulfate can be sold directly, there is no secondary pollution, the process is simple and easy to operate, and the capital and operating costs are low. The integrated design combining the byproduct generated from ammonia desulfurization treatment with that from the boiler ammonia desulfurization can further reduce the investment of the post-treatment system and simplify the process flow. This method simplifies the environmental protection emission control in these plants and benefits the plant operation management.